Right! First, a natatorium is a separate building. What you're telling me is you want this thing in a tiny cell that houses an entirely different building. You should change that to simply "swimming pool."

Nah, Slenderman was made wholesale by a Crepypasta photo+story contest over on the Something Aweful forums, IIRC. Mass death of children and a fire, linked to a distorted figure seen in two photos, in the distance.

Everything else came later, with the intent on making Slendy a creature that has always plauged hunanity.